1. Field of the Invention
The present invention relates to a controllable directional coupler having two optical waveguides formed in a substrate of electro-optical material on a surface of the substrate and extending parallel for a distance, and a control electrode structure formed on the surface and comprising a pair of control electrodes, the control electrode structure covering the two parallel waveguides.
2. Description of the Prior Art
Controllable directional couplers of the type generally set forth above, for example, in a substrate of LiNbO.sub.3, LiTaO.sub.3, InGaAsP or GaAlAs, can be employed as rapid modulators and switches as disclosed, for example, by R. C. Alferness, L. L. Buhl and M. D. Divino in the article entitled "Low-Loss Fibre-Coupled Waveguide Directional Coupler Modulator", published in Electronics Letters 18 (1982), pp. 490-491.